Antireflective coatings on eyeglass lenses such as oxidic coatings are desirable as they reduce the amount of bounce-back glare from the interior or concave surface of the lenses to the user's eye. Such coatings are especially desirable in sunglasses, which typically are used where lighting conditions are more intense and/or include glare or other optically undesirable properties. In particular, it is desirable to minimize reflection on the “wearer's side” of a lens such that a wearer is less likely to see a reflection of his own eye in a sunglasses lens. Prior art lenses often have an antireflective coating comprising an oxide applied at a thickness that is one-quarter the wavelength of a particular light frequency for which it is desirable to minimize reflection. As a result of this coating, one portion of the light is reflected from the surface of the antireflective oxidic coating and another portion of the light is reflected back from the interface between the antireflective oxidic coating and the lens surface. This well-known phenomenon results in destructive interference wherein there are two reflected waves of light, with each one-half wave out of phase with the other. Because the two waves of reflected light are one-half wave out of phase with one another, they interfere with, and cancel each other out. This cancellation of what would otherwise be reflected light reduces perceived light reflection at the cancelled wavelength.
One drawback associated with the prior art is that these prior art antireflective coatings typically reduce reflection at only a single wavelength. Reducing reflection associated with only a single wavelength or narrow range of wavelengths may impart a perceived hue or color to the lens that is associated with a color complementary to the blocked wavelength or narrow wavelength range. For instance, glasses which block a wavelength associated with the blue end of the visible spectrum may impart a yellow hue due to the remaining reflected light which has not been cancelled out. Although it is known in the art to provide a plurality of coatings that impede a plurality of wavelengths, there is a need to provide a set of antireflective coatings sufficient that impart antireflective properties onto the surface of the lens, canceling reflection of certain wavelengths without imparting a color to the lens and without significantly altering the viewed colors of images seen through the lens.
Although it is known in the optics art to provide antireflective coatings associated with a wider band of visible light, and such coatings may be applied to high-end optics in expensive cameras or microscopes, the costs associated with such coatings have heretofor been cost-prohibitive for sunglasses or the like. In addition, another drawback associated with prior art antireflective coatings is their lack of abrasion resistance, which is an essential property for use in sunglasses lenses.
Additional drawbacks associated with prior art antireflective coatings come from the current processes of applying the coatings. Plastic lenses absorb moisture and gases. Such lenses may also release moisture and gases and may even change size as they are heated or cooled. Variation in humidity, as well as gas and moisture absorption often inhibits consistent application of prior art antireflective coatings on plastic lenses.
Still another drawback associated with prior art methods for application of antireflective coatings to plastic lenses is the inability of plastic lenses to withstand the high temperatures commonly associated with the application of antireflective coatings. Polarized films used in association with sunglasses and the like are also sensitive to high heat and may not be able to withstand the high heat associated with many prior art antireflective coating processes. It would, therefore, be desirable to provide a reproducible method for applying a durable antireflective coating to plastic lenses, including those with polarizing film(s), under conditions that do not damage the lenses or polarizing film(s).
It is also known in the art to provide lenses with high contrast coatings. By suppressing the transmission of certain wavelengths through the lens (e.g., wavelengths near the blue end of the visible light spectrum), the contrast associated with the transmitted light is increased. This increased contrast translates into a sharper image being transmitted to the lens-wearer. One drawback associated with prior art high contrast coatings, however, is that such high contrast coatings, like the antireflective coatings, typically impart a color to the transmitted image. In accord with well-known optics principles, this imparted color is complementary to the blocked wavelength, and it may affect the trueness of image color that a wearer can perceive through a lens. As a result, many prior art sunglasses lenses with antireflective coatings distort colors in a manner undesirable to many sunglasses-wearers. It would, therefore, be desirable to provide a coating to a lens that blocks certain shorter bands of wavelength in a manner that increases clarity without imparting a colored hue to the transmitted image.
The difficulties encountered in the prior art described hereinabove are addressed by the present invention.